1. Field of the Inventions
The present invention relates generally to watercraft propulsion, and more specifically, to a watercraft propeller having a damper interposed between a propeller shaft and a blade of a propeller.
2. Description of the Related Art
A common watercraft propulsion device, such as an outboard motor, typically includes a propeller to produce thrust for propelling the watercraft. Some propellers incorporate a rubber damper interposed between a propeller shaft and blades. Such a propeller is disclosed, for example, in Japanese Patent Document No. JP-A-Sho 59-171789 (see pages 4 and 5, FIG. 1) (hereinafter “JP '789”). JP '789 discloses that the rubber damper can be used to dampen a shock experienced by the propeller shaft. Such a shock can be created, for example, when the propeller strikes an object such as a piece of driftwood or a rock located at the bottom of the sea while the watercraft moves in shallow water. The rubber damper helps to prevent damage to blade portions or members of a power transmission system. The rubber damper is interposed between an inner tube rotating with the propeller shaft and an outer tube having blades unitarily formed therewith and circumferentially positioned outside of the inner tube.
Japanese Patent Document No. JP-A-2000-280983 (hereinafter “JP '983”), discloses an outboard motor that has a rubber damper in a propeller power transmission system (pages 5 to 7, FIG. 7). The power transmission system disclosed in JP '983 is divided into a drive side and a driven side which meet at a portion between an engine and a propeller shaft. The rubber damper is placed at the portion where the system is divided. The rubber damper is provided to absorb a shock made during engagement of a dog clutch of a shift mechanism in the power transmission system. The rubber damper in JP '983 has a spring constant smaller than that of the rubber damper disclosed in JP '789. Thus, if any shock is transmitted to an operator of the outboard motor and passengers, it is through the outboard motor and the hull of the watercraft. Therefore, the rubber damper of JP '983 can tend to reduce the overall shock experienced by the watercraft operator and passengers, and ensure that any shock is as small as possible.
Nevertheless, the JP '983 rubber damper has such a small spring constant that it is unable to transmit the necessary torque to rotate the propeller at high speeds. Therefore, the outboard motor described in JP '983 also uses an engaging means. The engaging means limits the angular range through which two transmission members connected through the rubber damper can rotate relative to each other. The engaging means includes recessed portions formed in the one of the two metal transmission members, and protruding portions formed in the other transmission member. The protruding portions can engage with the recessed portions to limit the overall angular relative movement. Therefore, while the rubber damper in the outboard motor disclosed in JP '983 can dampen the shock made when the dog clutch engages, as the transmission torque increases, the power is directly transmitted from the one transmission member to the other transmission member through the metal recessed portions and the metal protruding portions which engage with each other.
The rubber damper disclosed in JP '789 can transmit the torque when the watercraft runs at a high speed. However, this rubber damper is not able to dampen the shock made when the dog clutch of the shift mechanism is engaged.
As mentioned above, the outboard motor disclosed in JP '983 can attenuate the shock by the rubber damper. However, even if some shock is momentarily absorbed by the rubber damper, the engaging means limits the angular relative movement of the two transmission members and thus prevents any further absorption of shock forces. Such a configuration can be problematic at high speeds.
For example, the engaging means ensure that power will continue to be transmitted from the engine to the propeller blades once the rubber damper has been maximally strained due to the engagement of the nesting metal protrusions and recesses. If the propeller strikes an object while rotating at a high speed with the metal portions of the engaging nested, some members of the power transmission system can be damaged. In particular, the propeller and other members that have relatively low rigidity are likely to be damaged.
The problem discussed above can be solved, to some extent, by mounting the propeller described in JP '789 to the outboard motor described in JP '983.
Employing such a structure is complicated however, and would require that the outboard motor have a first rubber damper disposed inside of a housing thereof and a second rubber damper disposed inside of the propeller. In order to accommodate both of the rubber dampers, the configuration of the outboard motor would have to have to be modified as well.